In radiosurgery or radiotherapy (collectively referred to as radiation therapy) very intense and precisely collimated doses of radiation are delivered to a target region (volume of tumorous tissue) in the body of a patient in order to treat or destroy tumors or other lesions such as blood clots, cysts, aneurysms or inflammatory masses, for example. Patients undergoing radiation therapy are typically placed on the treatment platform of a radiation treatment gantry. The radiation beam irradiates a region of interest in the patient, such as a diseased tissue including a tumor or cancerous growth site. When delivering the radiation, a plurality of radiation beams may be directed to the target area of interest from several positions outside the body.
The goal of radiation therapy is to accurately deliver a prescribed radiation dose to the tumor/lesion and spare the surrounding healthy tissue. The geometric accuracy of patient positioning relative to the treatment beam, as well as the location and amount of dose delivered to the patient is therefore important. There are a number of factors that could affect geometric and dose delivery accuracy, including but not limited to, radiation beam symmetry. A radiation beam which is not symmetric may introduce errors in the radiation beam delivered onto the patient.
Beam symmetry depends on the accurate alignment and placement of various mechanical elements/pieces of the radiation therapy system. Therefore, the mechanical elements need to be checked and tuned prior to the radiation treatment device being installed and/or used in the radiation treatment facility. Because the mechanical elements affecting beam symmetry tend to move, the beam symmetry needs also to be regularly checked and, if a shift or movement is observed from the mechanical elements' nominal preset values, the mechanical elements need to be adjusted and retuned during installment, and verified during regular preventive maintenance inspection. Also, the radiation dose amount and dose placement need to be sufficiently controlled for accurate patient treatment. Therefore, the radiation therapy machine itself needs to be properly tuned at the outset (on the production floor), and then continuously monitored through periodic checks, such as, during initial installation or during routine usage of the machine by the customer, to ensure that the system is operating within appropriate and expected parameters and standards, such as, but not limited to, standards prescribed by a nationally recognized regulatory groups, such as, the American College of Radiology (ACR), the American Association of Physicists in Medicine (AAPM), or the Society for Imaging Informatics in Medicine (SIIM), for example.
Electronic portal imaging devices (EPIDs) have been previously used for evaluating beam symmetry and for verification of treatment beams. Generally, these EPIDs are used as relative dose or absolute dose measuring devices, whereby images obtained using an EPID are compared with previously obtained images, and the discrepancies between the images are associated with the parameters of the system. However, in order to make such a comparison, the images must be corrected for non-linear behavior of the electronics, inhomogeneous pixel sensitivities, scattering in the detector, and the EPID panel's complex energy response. These correction methods are complex. For example, EPIDs used as relative dose measurement devices require an external reference measurement of some sort, and the corresponding calibration schemes are often tedious. EPIDs used as absolute dose measuring devices on the other hand require complex and time-consuming calibration techniques to correct for non-linearity of the EPID response. These calibration techniques also require accurate motion control of the EPID.
There is thus a need for methods, systems, and devices by which EPIDs can be used as measurement devices for beam symmetry and beam alignment without having to implement elaborate calibration procedures. Since many of the modern radiation treatment devices, such as medical LINACS, are equipped with electronic portal imaging devices (EPIDs), there is a need for a process that enables using the EPIDs as beam alignment measuring devices without extensive calibration protocols in place, in order to perform automatic calibration, tuning, and verification of the radiation treatment systems and devices. Since currently available radiation therapy machine tuning, calibration, and verification protocols are slow, inaccurate, require external hardware, and/or rely on subjective human decisions, this would reduce overall costs, processing, and analysis time, as well as remove operator dependency.